In rooms having sanitary fixtures, the room walls, for example in regions of bathtubs, shower stalls or the like, must be sealed absolutely tight which means that, before the application of tile to the wall, a watertight layer must be coated onto it as a base for the tiling. This sealing layer, however, is interrupted at the locations at which any buried fitting projects outwardly so that, in these regions, moisture can penetrate into the wall.